Pendant control for overhead cranes



Aug. 26, 1969 J. C. LESTER PENDANT CONTROL FOR OVERHEAD CRANES Filed Sept. 25, 1967 4 Sheets-Sheet l F .2. BY M, /VTTORNEY INVENTOR. JOHN C 1537257? J- C LESTER PENDANT CONTROL FOR OVERHEAD CRANES Aug. 26, I 1969 Filed Sept. 25; 1967 4 Sheets-Sheet 2 INVENTOR. Jamv C 55752 Aug. 26, 1969 J. c. LESTER PENDANT CONTROL FOR OVERHEAD CRANES 4 Sheets-Sheet 3 H1! Sept. 25, 1967 INVENTOR- Jomv C. 1537-5? 1% ATTORNEY.

Aug. 26, 1969 J. c. LESTER 3,463,327

PENDANT CONTROL FOR OVERHEAD CRANES Filed Sept. 25, 1967 4 Sheets-Sheet 4 v INVENTOR. 'J Joy/v C" 15575? v BY United States Patent U.S. Cl. 212-21 7 Claims ABSTRACT OF THE DISCLOSURE This invention is an improvement in overhead traveling crane pendant controls of the type employing heavy and large pendants with pushbuttons operable for sending 110-220 volt signals to a controller on the crane through one or more heavy, relatively stiff and unwieldy, multiwire cables.

The improvement is characterized in that the large pendants and cables which have been employed heretofore are replaced by a single light flexible coaxial cable connected at one end to a controller on the crane and at the other end to a small light pushbutton pendant having a plurality of pushbuttons. Each pushbutton controls a low voltage energizing circuit for an oscillator which, when activated, emits a signal of predetermined radio frequency different from the frequency of the oscillators controlled by the other pushbuttons. These signals are transmitted over the coaxial cable to receivers on the c011- troller. Each receiver has a frequency response corresponding to a different one of the oscillators, and each is connected in a different control circuit from the others and controls a different power switch for causing a selected operation of the crane motors.

This invention relates to remote pendant controls for overhead traveling cranes.

Heretofore remote pendant controls have been used in connection with overhead traveling cranes for controlling numerous operations, such as travel of the bridge in opposite directions, the traverse of the trolley in opposite directions, the raising and lowering operation of the hoist mechanism, sounding audible warning signals, and the like. In addition to these basic operations, quite often different speeds in each direction of operation of the bridge, trolley, and the hoist mechanism are to be selected. Consequently, the pendant control must be capable of sending to the controller on the crane bridge from eight to thirty control signals, selectively, depending on the particular type of crane installation and its functions. These signals are created by operation of pushbuttons on the pendant, one signal for each pushbutton, or one signal for each step in case of stepped pushbuttons such as used for providing :a plurality of speeds.

The typical pendant control generally comprises a multi-wire cable of which individual wires are connected at their upper ends to respective terminals of the controller of the crane and at their lower ends to the pushbuttons, respectively. Generally, the circuit employs a common ground wire and individual wires, one for each pushbutton. The prior control circuits employ 110 or 220 volts, requiring rugged and large pushbutton operated switches with strong return springs which must be held depressed by the operator.

If the usual number of these different selective operations are to be controlled by the remote pendant control, the cable necessarily becomes quite large in diameter and relatively stiff, and consequently cumbersome for manipulation by the operator. If the crane bridge is even the usual minimum distance above the floor, the weight of the cable itself requires an expensive and complicated counterbalance mechanism on the crane, generally of the spring driven drum type, onto which a flexible Weight sup- ICC porting cable or chain, connected at its lower end to the control cable, or pendant, is wound. These counterbalances require frequent servicing and repair.

Such control cables contain a large number of the wires disposed a considerable distance outwardly from the cable axis. Since the cable is repeatedly warped or curved and flexed by the operator in normal operation, the wires are subjected alternately to compressive stresses when at the inside of the bend and tension when at the outside of the bend. The larger the diameter of the cable, the more pronounced are these stresses. Such temporary warping, curving, and flexure occur frequently as the operator lifts the pendant over obstructions on the floor of the worksite, or swings it laterally to avoid them. The resultant stresses contribute to fatigue of the wires and breakage thereof with a resultant shortening of their useful lives.

The manipulation of the pendant while following the crane bridge and trolley and while manipulating the spring resisted pushbuttons is very burdensome and tiring. Frequently, the operator must stop the crane and relieve his arms and fingers from this combined burden.

Servicing of this type of pendant is very expensive and time-consuming due to the massiveness of the cable and the heavy counterbalancing mechanism required. Usually servicing requires the erection of expensive scaffolding on the worksite floor, disconnection of each cable wire individually at both ends, and installation of a new cable, and then reconnection of each of the wires at both ends.

In many installations, a single multi-wire cable is too large and stiff to be practical and in such cases two multiwire cables are used, each connected to an individual pendant, the two pendants being clamped together for convenience in handling as a unit.

All of these disadvantages are overcome by the present invention wherein, instead of the prior multi-wire cables, a simple coaxial cable is employed. The pushbuttons are electrically connected to electrical oscillators, respectively, which are disposed in the pendant. Each oscillator, upon depressing its associated pushbutton, is activated and emits an electrical signal of predetermined radio fre quency different from the frequency of each of the signals of each of the other oscillators. These signals are then transmitted through the same coaxial cable to complementary frequency responsive receivers at the controller, each receiver being responsive to a different oscillator frequency. Each receiver controls an associated relay or switch which, in turn, controls a selected power switch of the controller.

This arrangement makes possible the use of a pendant small diameter coaxial cable which is readily flexible, thus permitting shorter radius bends while greatly reducing the stresses tending to cause metal fatigue in the cable. The cable is light enough so that the counterbalancing mechanism is not required. The pushbuttons and signal producing oscillators and circuitry operate at very low power levels and at very low voltages,for example, 9 to 24 volts D.C., whereby very light restoring springs can be used for the pushbuttons so that the pushbuttons can be held closed by very light finger pressure. Consequently, the entire pendant is easily manipulated without tiring the operator.

As a comparative example of a prior installation, on a large overhead traveling crane, the pendant control and multiwire cable have a combined weight of 65 pounds, Whereas the present pendant control and coaxial cable for effecting the some operations have a combined weight of only one pound.

Whereas replacement of the conventional cable requires that each wire of the old cable be disconnected at both ends and each wire of the new cable be connected at both ends, replacent of the present coaxial cable requires only that the upper end and the lower end each be disconnected from a single fitting, the damaged cable removed, and a new cable connected to a single fitting at each end.

Because the cable is of light weight and can be handled readily by workmen, it can be installed and removed without the necessity of erecting heavy scaffolding and platforms on which to work during any replacement.

Coaxial cables have been used heretofore for sending a number of signals of different frequencies over the same cable, concurrently or selectively. In the present case, the usual advantages of using a coaxial cable are retained and, in addition, other advantages result and many problems peculiar to pendant controls of overhead cranes are overcome or eliminated by the simple combination with such crane controllers of a coaxial cable and a pendant carrying associated frequency signal device.

Various other objects and advantages of the invention will become apparent from the following description wherein reference is made to the drawings, in which:

FIG. 1 is a diagrammatic illustration of an overhead traveling crane and a remote pendant control embodying the principles of the present invention;

FIG. 2 is a block diagram illustrating the remote pendant control, controller on the crane, and the control circuitry operatively connecting pushbutton operated transmitting modules on the pendant to receiving modules on the controller on the crane;

FIG. 3 is an enlarged block diagram illustrating a typical receiving module of the pendant control and its functional relation to a motor of the crane;

FIG. 4 is a wiring diagram illustrating a transmitting module of the pendant control;

FIG. 5 is a wiring diagram illustrating the control circuitry, including receiving modules of the pendant control;

FIG. 6 is a wiring diagram showing in more detail the circuitry of the remote pendant control;

FIG. 7 is a wiring diagram showing in more detail the circuitry of the receiving controller; and

FIG. 8 is a wiring diagram of a radio frequency detector used in the invention.

Referring to FIG. 1, a conventional overhead traveling crane 1, operable on rails 2 at the worksite, is illustrated. The crane 1 comprises a traveling bridge 3 having wheels 4 by which it is supported for travel along the rails 2. A trolley 5, having wheels 6 by which it is supported for travel along the bridge on suitable rails 7 on the bridge, carries a hoist mechanism 8. Electric motors 9, and 11 are provided, the motor 9 for driving the bridge 3 in opposite directions along the rails, the motor 10 for traversing the trolley 5 in opposite directions on the bridge, and the motor 11 on the trolley for operating the hoist mechanism 8 so as to raise and lower its hook 12. In general, such cranes employ suitable trolley wires and trolley wheels for conducting power to the various motors while permitting concurrent movements of the bridge, trolley, and hoist.

Generally the travel motor 9 is carried on the bridge, and the traverse motor 10 and hoist motor 11 on the trolley. All motors are controlled by a suitable controller 14 located on the bridge and containing the customary relays and power switches which are operable to connect the motors in selected circuits with the source of power supplied through suitable trolley lines and wheels. Conventional relay controlled motor driven audible signals, not shown, also are carried on the crane.

The present invention is directed particularly to the remote pendant type control for operating the controller 14 on the bridge so as to cause it to connect the motors in various power circuits, selectively. In the form illustrated, the pendant control comprises a remote pendant 15 connected to the lower end of a coaxial cable 16 having an outer shielding conductor 16a and an axial conductor 16b, as illustrated in FIG. 2. At its upper end, the

cable is connected to an input terminal on the controller 14.

The pendant 15 comprises a pushbutton housing 17 which carries a plurality of normally open, spring restored, pushbutton operated switches 18. Each switch 18 is connected through a master switch 29, and radio frequency choke 92, later to be described, an axial conductor 16!) of the coaxial cable 16 and controls the application of DO supply therefrom to an associated radio frequency generating and transmitting module 19. The cable 16 is arranged to be connected to a low voltage source so that, upon closure of any selected one of the switches 18 while operating voltage is being applied to the coaxial cable 16, the associated module 19 is activated. Each module 19, when activated, emits a signal of predetermined radio frequency fed through conductors 34 and 35, later to be described, and inner and outer conductors 16a and 16b of the coaxial cable. The emitting modules 19 are arranged one for each pushbutton switch 18, and each module 19 emits a signal of different radio frequency from each of the others. Each module 19 is a crystal controlled transistorized oscillator which may be powered at the low voltage, such, for example, as 24 volts, supplied through the coaxial cable 16. It preferably generates a preselected radio frequency in a range from 300 kc. to 2 mc.

correspondingly, in the controller 14, frequency responsive modules 20 are provided, one for each motor power switch, or for each relay controlling a power switch. As illustrated in FIG. 3, each frequency responsive module 20 of the controller includes a crystal controlled transistorized detector 21 and oscillator 23. Each detector-oscillator combination 21-23 is selected so that it is responsive to the frequency of a different one of the modules 19 to provide an audio beat signal as later described herein.

Thus, upon closure of any pushbutton operated switch 18, its corresponding frequency responsive module 20 in the controller 14 causes operation of a selected power switch directly or of a relay which, in turn, controls a power switch, and thereby causes a preselected operation of a preselected one of the motors; for example, operation for forward and reverse bridge travel, forward and reverse trolley traverse, raising and lowering hoist motions, each at selected speeds, and for signal sounding, and the like.

Each of the motors 9, 10 and 11 may be connected in the same manner, the manner of connection being dictated by the use requirements for the particular crane. For example, in FIG. 2, the motor 9 is shown with four connections as follows: forward, reverse, high speed, low speed. For brevity in illustration, the connections to the other motors 10 and 11 are not shown, as they may be the same as those for motor 9, but there is included a connection to a motor powered signal device S. The specific connections to the motors 19 and 11 and any other motors could be the same connections as the motor 9, or other connections as required.

An example of a receiving module and associated devices of the controller 14 is indicated by the block diagram of FIG. 3, which shows the control by a single frequency responsive module 20 for one operation of the motor 9; for example, forward at normal speed. Since each module 20 is provided with like associated devices and circuitry, only one is described herein in detail.

The transmitting modules 19 provide outputs spaced apart from each other in frequency at least 15 kc. The responses of the receiving modules 20 correspond in frequency to the outputs of the transmitting modules 19, respectively, being spaced 15 kc. apart from each other.

Each detector-oscillaor combination 21-23 acts as a discriminator and accepts only, or responds only, to signals of radio frequency, plus or minus 1 kc., and each has its input connected to the axial conductor 16b of the coaxial cable 16 and its output connected to a mixer 22 as shown in the block diagram of FIG. 3. In each module 20 the local oscillator 23 supplies current at from 200 kcs. to 2,000 kcs. frequency to the detector 21. The detector 21 and the mixer 22 combine the radio frequency signal sent through the coaxial cable from the transmitting module 19 with the oscillator signal from the local oscillator 23 to produce an audio beat frequency which is equal to the center pass band frequency of response of a tone sensitive audio amplifier 24. The mixer detector 21, 22 combines the radio frequency signal sent through the cable from the transmitting module 19 with the oscillator signal from the local oscillator 23 to produce an audio beat frequency which is equal to the center pass band frequency of response of a tone sensitive amplifier 24. The audio beat of the mixer 22 is fed to the tone sensitive amplifier 24 which amplifies the audio beat and feeds the amplified signal to an audio DC converter 25 which develops a DC output in response to the audio beat frequency. The DC converter 25, in turn, operates a relay 26 which, in turn, energizes a relay 27 which connects the magnet of a power switch 28 for the motor 9 to a source of power. The switch 28 is one of several customarily provided in a traveling crane controller. Thus, so long as the pushbutton associated with the described module 20 is depressed so as to close the associated switch 18, a radio frequency signal is transmitted along the coaxial cable from the transmitting module 19 to the receiving module 20, and the associated power switch for one of the motors is operated so as to connect the motor through suitable circuitry to the high voltage source of power for operation at a preselected speed in a preselected direction.

Each motor may be connected to the power source through various circuits, each controlled by a different associated control relay in a conventional manner for connecting it for different speeds forward or reverse, and the like, one relay usually being provided for each connection.

Frequently, where more than one speed is required in any direction, the pushbutton is of the stepped type, having a number of switches 18 operable successively by the same pushbutton, the particular switch operated at any given time depending upon the degree of depression of the pushbutton. These stepped pushbuttons may be considered as separate pushbuttons and, if desired, separate pushbuttons can be used for each speed.

The power for operating the transmitting modules may be at a potential in the neighborhood of 12 or 24 volts DC, and supplied to the transmitting modules 19 from a voltage supply source on the controller through the coaxial cable 16.

If desired, a master switch 29 may be provided in the pendant housing 17 for connecting the low voltage source of power to, and disconnecting it from, the transmitting modules 19.

From the foregoing it is apparent that by the use of radio frequency transmitting and receiving modules and associated localized circuits for each, a coaxial cable can be used instead of the conventional multi-wire cable heretofore provided for the control of the crane from a remote pendant control station.

By virtue of this change in the pendant control in this particular combination with an overhead crane, an extremely light and flexible cable can be used. Due to the low voltage employed, very light pushbutton operated switches can be used, and their self-restoring pushbuttons can be manipulated and held in closed position by the fingers of the operator without tiring the operator.

The expensive counterbalances which require frequent servicing are totally eliminated.

The coaxial cable will serve for a much longer time than conventional cables without failure and without erratic operation.

The conventional multi-wire cables customarily employ or 220 volt circuits. Consequently, due to possible short-circuits in the cable upon breaking of one or more wires, there is a constant direct danger to the workmen and equipment, and danger of throwing the crane out of control while leaving it connected to the source of power.

Broadly, the main advantages of the invention are attained by the use of the radio frequency signals transmitted by means of the coaxial cable to receivers at the controller on the crane inasmuch as only a single pair of conductors are involved in the transmission, the outer conductor acts as a shield prevention unwanted interfering pick-up of extraneous static or like signals, and preventing radiation of signals from the cable. However, some specific advantages reside in the specific circuit here employed, which is illustrated in FIGS. 4 through 7, and which is as below set forth:

Referring to FIG. 4, each transmitting module 19 comprises a number of enclosed components and is less than /2 cubic inch in volume. Each module includes a quartz crystal 30 which may be of the sub-miniature type and three ceramic disc capacitors 31, 32, and 33, each preferably of fifteen picofarads. Flexible leads 34 and 35 lead from the module and connect it to the lines 16a and 16b of the coaxial cable 16 while flexible lead 36 connects the module to the associated switch 18 controlling the application of power supply to the module for bring it selectively into operation, as illustrated in FIG. 2. A transistor 37 of the NPN silicon type is employed and is connected to the capacitors 31, 32, and 33 and .to a pair of resistors 38 and 39, as illustrated, the resistor 38 being 100,000 ohms and the resistor 39 being of the order of 470 ohms. Each resistor 38 and 39 may have a thermal capacity of A1 watt. The resistor 38 connects the base of the transistor 37 to the conductor 36, the resistor 39 connects the emitter of the transistor 37 to ground, and the crystal is connected across the base and collector of the transistor.

The capacitor 32 is connected between the leads 34 and 35, the lead 35 being connected to ground. The capacitor 33 is connected between ground and the base of the transistor 37, and the capacitor 31 connects the collector of the transistor 37 to the lead 34. A radio frequency choke coil 40, which may be of 2 /2 mh., is connected at one end to the common terminal of the crystal 30 and the capacitor 31 and at the other end to the lead 36.

The above structure provides a transistorized oscillator the frequency of oscillation of which is controlled by the quartz crystal 30. A typical frequency with these components is in the 9 mh. range. Thus, upon closing of the switch 18 for any one of the transmitting modules 19, a selected radio frequency is impressed upon the coaxial cable.

Referring next to FIG. 5, the circuitry of the receiving and decoding unit is illustrated. This unit comprises essentially six basic elements including the local crystal controlled oscillator 23, the transistorized mixer 22, tone sensitive amplifier 24, audio to DC converter 25, and DC amplifier and relay 27, the delay serving for connecting the associated motor power contact switch to a source of power.

The local oscillator circuit 23 comprises a quartz crystal 45 with a frequency equal to that of the corresponding transmitting module crystal 30, plus or minus 4 to 1,000 cycles per second. A silicon transistor 46, or equivalent, is provided. A suitable radio frequency choke coil 47 and capacitors 48, 49 and 51] are included in the circuit as shown. The emitter of the transistor 46 is connected to ground through a resistor 51. The output of the local oscillator 23 is fed through a lead 52 to the emitter of a high frequency transistor 53 to the base of which the signal of the coaxial cable is also fed through a capacitor 54. A plurality of resistors 55, 56 and 57 are connected in the circuit as shown. A radio frequency choke coil 58 is connected at one end to the collector of the transistor 53. The other end of the choke coil 58 is connected to a parallel circuit including a capacitor 60 and a primary coil 61 of a transformer, which, in turn, are connected to a common ground 62. A secondary coil 63 of the transformer is connected to an audio frequency transistor 65, or equivalent. Suitable resistors 66, 67 and 68 are connected in the circuit, as also are capacitors 69 and 70, thus providing the audio amplifier 24. The amplifier 24 is connected to a primary coil 71 of an audio transformer 25. The companion or secondary coil 73 of the audio transformer is connected to a transistor 74. A suitable resistor 75 and capacitor 76 are connected in the circuit with the transistor 74, as illustrated, as also is a resistor 77. The signal from this circuit is fed to a base of a transistor 80 which is preferably a medium power switch transistor or equivalent from which a signal is supplied to one end of the coil 81, the opposite end of the coil being connected through a line 82 to the negative side of a 6-volt power source 83. The coil 81 operates a relay 84 which closes a circuit through leads 85 and 86 from a 24-volt source 87 (FIG.

7) through a coil 88 which operates a power switch for the particular operation of the motor 9.

This circuitry can be connected to the source of power 87 only when a radio frequency detector 90 with built-in relay is operative and it is operative only when radio frequency is present in the coaxial cable.

The manual switch 29 as best illustrated in FIGS. 2 and 6, connects the transmitting modules 19 to a source of power, by way of the switches 18, through a radio frequency choke coil 92, this power being supplied through the'axial conductor 16b and the outer sheath 16a of the coaxial cable.

In operation, the signal from the local oscillator 23 is injected into the transistor 53 through the capacitor 48, as shown in FIG. 5. This frequency may be, for example, 9 me. The signal from the associated transmitting module 19 in the remote pendant is coupled to the base of the transistor 53 by way of the coaxial cable and through the capacitor 54. This may be a frequency of 9 me. plus 500 cycles per second. This signal is amplified by the transistor 53 and mixed with the 9 mo. signal injected into the transistor 53 by the local oscillator 23. These two signals are mixed in the transistor circuit 53 of the mixer 23 to obtain a beat frequency of 500 cycles per second. This 500 cycles per second beat frequency is passed through the radio frequency choke coil 58 and the primary winding 61 of the audio transformer 61a. The choke 58 prevents the radio frequency signals from entering the audio transformer 61a. The capacitor 60 helps to limit the response of the transformer 61a and also bypasses any radio frequency signals that may possibly pass through the radio frequency choke coil 58. The resistors 55 and 56 form a bias network for the base of the transistor 53. The resistor 57 performs a circuit limiting function for the transistor 53 and is also a load resistor and an isolating resistor for the signal from the local oscillator circuit 23. The transistor 53, due to its small emitter to base capacitance, also serves to isolate the local oscillator signal and prevent its being transferred back into the coaxial cable by way of the base of the transistor 53 and the capacitor 54. For this reason, diode mixers generally are not suitable. The capacitor 54, due to its high reactance at audio frequency, tends to eliminate noise pulses from entering the transistor 53.

The current at 500 cycles per second frequency passing through the primary winding of the transformer 61a induces a signal in the secondary winding of the transformer which is further amplified by the transistor 65 of the audio amplifier 24. Resistors 66 and 70 form the base bias network for the transistor 65 and the resistor 68 acts as a circuit limiting device for the transistor 65. The capacitor 69 serves to couple the audio frequency from the secondary of the transformer 61a to the emitter of the transistor 65. The capacitor 70 tends to limit the frequen' cy of response of the transistor 65. The 500 c.p.s. signal now amplified by the transistor 65 is coupled through an audio transformer 71-73 to the base of the transistor 74 of the audio to DC converter 25. Since the base of the transistor 74 is connected to ground, which is at a negative potential with respect to the collector, the transistor 74 can only conduct current on the positive going part of the 500 c.p.s. signal coming from the secondary of the transformer 25. The capacitor 76 is used to smooth out this pulsating DC to a smooth DC signal. The transistor 74 is coupled to the base of the transistor through a current limiting resistor 75. The base of the transistor 80 is coupled to its own emitter through a resistor 77. Resistors 75 and 77 form a load for transistor 74, as well as the bias network for the base of the transistor 80. When the transistor 74 receives the 500 c.p.s. signal from the secondary of the audio transformer 61a it becomes conducting, i..e, turns on. This places a negative bias on the base of the transistor 80 through the resistor 75.

Since the combined resistance of the resistor 75 and transistor 74 when in its ON or conductive state is much less than that of the resistor 77, the transistor 80 is forward biased and becomes conductive. When the transistor 80 becomes conductive, the relay coil 81 is energzed, thereby closing the relay contacts 84. Upon the loss of 500 c.p.s. signal from the secondary 73 of the audio transformer in the connecter 25. The transistor 74 is immediately reverse biased, due to a lack of positive signals from the secondary 73 of the audio transformer, and the low DC resistance of the transformer 71-73 now causes a reverse bias at the base of the transistor 74,

Since the transistor 74 is now non-conductive or OFF, the combined resistance of the transistor 74 and resistor 75 is much more than the resistance of the resistor 77, thereby causing a reverse bias at the base of the transistor 80. This turns the transistor 80 off. Since the relay coil 81 is no longer energized, the relay contacts 84 open under the influence of a return spring or gravity. A pass band of the audio section described is limited from a lower value of 200 c.p.s. to a high value of 5,000 c.p.s.

In general, in the operation of the system, it is assumed that a power supply 93, and the power supplies 83 and 87, are supplied with power from the main 1l0-volt AC, 250-volt DC lines, or whatever power lines are available. Assuming the cable 16 is properly connected to pendant 17 and to the control unit 14, the operator may close the master switch 29.

Referring particularly to FIGS, 6 and 7, when the switch 29 is closed, a Zener diode is connected across the coaxial cable 16, thus holding the line voltage at 9 volts. The open line voltage, as seen from FIG. 7, was originally 12 volts DC and supplied by supply 93. The current flowing through the cable energizes a coil 96a of a safety relay 96, thereby to cause closure of contacts 96b. Meanwhile, due to the voltage across the coil 98a of a second safety relay 98, its contacts 98b are closed. The contacts 98b and 96b are now closed, to partially complete the power supply circuit for the receiving modules 20, but the circuit remains open at the normally open contacts 10% of a relay 100.

Assume that the operator now closes one of the pushbutton switches 18. This energizes the radio frequency oscillator of the module 19, thereby emitting a 9 me. plus 500 c.p.s. signal to the coaxial cable. Upon detecting this signal, the radio frequency detector 90 energizes the coil 100a of the relay 100 having the normally open contacts 100]; as indicated in FIGS. 7 and 8, thereby closing the normally open contacts 1001) allowing power from the power source 87 to feed into all of the receiving modules 20. At the same time, the relay coil 81 contained in the receiving module 20 corresponding to the activated one of the modules 19 is energized. No other relays are pulled in at this time, as is apparent from the circuitry hereinbefore described. This same sequence of operation follows when corresponding pushbuttons 18 are operated. Further simultaneous operation of several pushbutton switches 18 to provide corresponding concurrent signals is possible but in certain cases, where such is desired to prevent concurrent generation of signals, the pushbutton switches 18 may be connected as shown for the two uppermost switches of FIG. 6.

The circuitry of the detector 90 as shown in FIG. 8 comprises a full-wave diode bridge or rectifier 102 connected across the conductors 16a and 16b of the coaxial cable 16 through a pair of capacitors 104. The DC output of the rectifier 102 is impressed across the base and emitter terminals of the NPN transistor 105 having its collector terminal connected through a pair of series-connected resistors 106 and 107 to the emitter terminal of a PNP transistor 109. The base terminal of the transistor 109 is connected to a junction intermediate the resistors 106 and 107, and the collector terminal of the transistor 109 is connected through the coil 100a of the relay 100 to the emitter terminal of the transistor 105. Additional stages of amplification may be provided in similar fashion to provide sufiicient gain to operate a relay of appropriate size.

Certain safety features are involved. For example, assuming the operator leaves the main switch 29 in ON position, the crane remains in safe condition since the relay contacts of the detector 90 are open, thereby disconnecting power supply 87 from the receiving modules 20 as well as from the relays which operate the power switches for the various pieces of equipment, such as the motor 9.

Assuming that the coaxial cable should become shortcircuited, there would be no radio frequency signal to the detector 90 and there would be no, or very little, DC voltage on the safety relay coil 9801. Therefore, with the safety relay coil contacts 98b and the coil for safety relay contacts 10% and 1000 both open, all power to the motion relays for operating the main switches of the power equipment is cut off.

Assuming the coaxial cable becomes open and by some remote possibility a radiated radio signal of the proper frequency enters into the system, since the wire leading from the transmitting module 19 is now open, no current flows to the safety relay coil 96a and its contacts 96b are therefore open, removing all power from the coils 88 of the motion relays. It is, therefore, obvious that three discrete conditions must be satisfied before any motion can occur, as follows:

(a) A predetermined DC load must be connected to the system, it normally being provided by Zener diode 95;

(b) Proper DC voltage must exist between the axial conductor 16b and the outer shield 16a of the coaxial cable to keep the contacts 98b of the safety relay 98 closed; and

(c) Audio frequency signal of the proper frequency must be detected by one or more of the receiving modules 20.

Having thus described my invention, I claim:

1. A pendant control for overhead travelling cranes wherein an electric controller is carried on the bridge and includes a plurality of control mechanisms for operating power switches on the crane upon energization of the mechanisms, thereby to control the crane; and comprising radio frequency receivers adapted for connection to the mechanisms, respectively, each receiver being responsive to radio frequency signals within a predetermined range dilferent from the range of the radio frequency signals to which the other receivers are responsive, and each receiver being operative upon receipt of a signal within its predetermined frequency range to cause energization of its associated mechanisms;

radio frequency transmitters operable when enerized by low voltage to emit radio frequency signals, respectively, the signal of each transmitter being within the range of reception of a different one of the receivers;

means responsive to the transmitters for connecting the transmitters to a source of voltage sufficiently low so that shock hazards are not presented, and including means for activating the transmitters, selectively;

characterized in that a coaxial cable is provided and all of the transmitters are connected to one end of the cable and all of the receivers are connected to the other end of the cable, and

a pendant is mounted on said one end of the cable, and

the transmitters are carried by the pendant.

2. A pendant control in accordance with claim 1 wherein each radio frequency receiver includes a local oscillator and a mixer, each oscillator provides a signal of a frequency different from the frequency of the signal to which its associated receiver is responsive, each mixer is connected to combine the signal from its associated oscillator with the radio frequency signal received by its associated receiver through the coaxial cable thereby to provide a beat signal, and each receiver includes a circuit responsive to the beat signal provided by the mixer thereof.

3. A pendant control in accordance with claim 1 wherein the control mechanisms are electrically powered through a normally open power supply circuit, and safety means are provided for closing the power supply circuit so as to render the control mechanisms energizable only when a signal of radio frequency and of adequate voltage to operate the receivers is present in the coaxial cable.

4. A pendant control in accordance with claim 3 wherein the safety means includes a radio frequency detector connected across the coaxial cable and having circuit completing means interposed in the power supply circuit.

5. A pendant control in accordance with claim 3 wherein the safety means includes a Voltage responsive means having an operating means and a circuit closing means, the voltage responsive means being connected across the coaxial cable and the circuit closing means being interposed in the power supply circuit.

6. A pendant control in accordance with claim 3 wherein the coaxial cable is connected to a source of power through a supply lead, and the safety means comprises a current responsive means having an operating means and a circuit closing means, the operating means being interposed in the supply lead to the coaxial cable and the circuit closing means being interposed in the power supply circuit.

7. In combination,

an overhead travelling crane including a bridge;

operating power switches on the crane;

a plurality of control mechanisms on the bridge for operating the power switches upon energization of the control mechanisms thereby to control the crane;

a coaxial cable carried by the bridge with a portion thereof suspended below the bridge;

radio frequency receivers connected to the mechanims, respectively, and to the upper end of the cable, each receiver being responsive to radio frequency signals within a predetermined range different from the range of the radio frequency signals to which the other receivers are responsive, and each receiver being operative upon receipt of a signal within its predetermined frequency range to cause energization of its associated mechnism;

radio frequency transmitters connected to the lower end of the cable for transmission therethrough to the receivers and operable when energized by low voltage to emit radio frequency signals, respectively,

1 1 the signal of each transmitter being within the range of reception of a difierent one of the receivers; means responsive to the transmitters for connecting the transmitters to a source of voltage sufiiciently low so that shock hazards are not presented, and including means for activating the transmitters, selectively; and a pendant mounted on the lower end of the cable and supporting said transmitters.

References Cited UNITED STATES PATENTS 2,379,631 7/1945 Finckh 340171 2,886,750 5/ 1959 Vogel 318-16 3,201,757 8/1965 Himmel 340171 3,200,959 9/ 1965 Miller 340-171 3,263,141 7/1966 Nicola n 340-171 3,351,945 11/1967 Borsattino 340-171 EVON C. BLUNK, Primary Examiner H. C. HORNSBY, Assistant Examiner US. Cl. X.R. 

